Generally speaking, liquid foods such as fruit juices, cooking oil, wine etc., which are nowadays often packed and stored in packages of the single-use type (so-called disposable cartons), are products which are highly sensitive to the effects of oxygen and are flavour-sensitive products which are destroyed or tainted if they are exposed to the action of oxygen. Consequently, one minimum requirement placed on such disposable packages is that they must be as impermeable to oxygen as possible and, ideally, completely oxygen-tight in order to be able to provide the best possible protection against oxygen and thereby flavour protection to the packed products.
One packaging material which is often employed in disposable packages for such oxygen- and flavour-sensitive products consists of a plurality of layers laminated to one another and comprising a carrier layer of paper or paperboard and an aluminium foil bonded to one face of the carrier layer (corresponding to the inside of the finished package), the aluminium foil rendering the material practically impermeable to oxygen, and an outer protective polyethylene coating to avoid direct contact between the aluminium foil and the product which is to be packed.
Disposable packages which are produced from a packaging material including an aluminium foil possess extremely good tightness properties vis-a-vis oxygen, but, on the other hand, provide a more or less limited flavour protection to the packed product, in particular if this consists of citrus fruit juice or other fruit juices. One of the reasons for the defective flavour protection afforded by such a package could probably be traced to the protective polyethylene coating of the packaging material which, hence, is in immediate contact with the packed product and, because of its non-polar nature, at least to some degree absorbs, ingests and retains flavour or odour ingredients of a more or less non-polar nature of the type occurring in the above-mentioned types of juice products. For example, it has proved that the concentration of the non-polar flavour ingredient d-limonene gradually fades in the packed juice product and, in time, becomes so low that a manifest deterioration occurs in the flavour of the packed product. In addition, the material costs of the prior art packaging material are inescapably high because of the fact that it uses aluminium - a very expensive metal.
Consequently, the packaging technology art has long been in need of being able to develop an aluminium-free packaging material with superior tightness properties vis-a-vis oxygen and at the same time superior barrier properties against, or low absorption of, flavour and odour ingredients.
One such aluminium-free packaging material is disclosed in, for example, U.S. Pat. Ser. No. 4,701,360. This prior art packaging material is also of laminate type and includes a carrier layer of paper or paperboard and a layer of ethylene vinyl alcohol copolymer (EVOH) serving as oxygen and flavour barrier. A barrier layer of this type enjoys several merits. It possesses tightness properties vis-a-vis oxygen and has, moreover, (because of its polar nature) good barrier properties or low absorption tendencies in respect of non-polar flavour and odour ingredients, for example d-limonene, at the same time as being a material approved for direct contact with foods and, as a result, needing no additional protective coating. Furthermore, EVOH is a cheaper material than aluminium.
However, a packaging container with an inner barrier layer of EVOH in contact with the packed product has but slight barrier properties vis-a-vis polar flavour and odour ingredients, e.g. fruit alcohols which occur in citrus fruit juices and other fruit juices and which, thus, tend to migrate into and be ingested by the barrier layer at the same time as the packed juice loses its flavour to a corresponding degree. The problem inherent in the absorption of polar flavour and odour ingredients can, however, be solved by, for example, coating the barrier layer with an outer protective coating of non-polar material, for example polyethylene, as described in U.S. Pat. Ser. No. 4,789,575, but this prior art solution merely substitutes this problem with a new flavour problem in analogy with the above reasoning relating to the prior art packaging material with polyethylene coated aluminium foil.